This project is for a series of analytical studies based on data from the National Household Survey on Drug Abuse (NHSDA). In each of these analytical studies, the research team specifies a set of discrete etiologic and epidemiologic hypotheses for testing and evaluating against the epidemiologic data gathered as part of the on-going NHSDA. For example, the most recently completed project involves a set of hypotheses about the characteristics of 12-17 year old youths who are just starting to take marijuana. This resurgence of youthful marijuana use is cause for concern throughout NIDA and the PHS, and may be an indication of a new epidemic period of marijuana involvement. Our hypotheses address both individual-level determinants of marijuana initiation (e.g., conduct problems), family-level determinants (e.g., family SES), and community-level determinants (e.g., urban versus suburban versus rural environment). In the course of this project, we are looking specifically for evidence that the epidemiologic profile of recent-onset marijuana users has changed from the mid-1980s to the mid-1990s, in anticipation that this changing epidemiologic profile will provide clues toward understanding the dynamics of this epidemic phenomenon. Our goal is to make a rapid translation of these new epidemiologic and etiologic findings into experimental research and ultimately into practical public health strategies for prevention of teenage marijuana use. Another project involves an attempt to replicate findings from the National Comorbidity Survey that concern etiologic sub-types of drug dependence, with a focus on creating etiologically more homogeneous categories of drug dependence defined in terms of affective disturbances and in terms of antisocial behavior or conduct problems. To a large extent the NCS dataset is more powerful because it has more complete diagnostic assessments. However, the NHSDA has strengths of its own (e.g., a much larger sample size), which make it highly appropriate for attempts to replicate the NCS findings. The branch anticipates a continuing series of these analytic projects, seeking to extract new and useful information from already available epidemiologic data that are being gathered each year at considerable expense to the Public Health Service. Whereas the PHS now generally uses these data only to produce cross-tabulations that describe the nature and extent of drug use in the United States (e.g., the proportion of youths and adults who are recent drug-takers), our work on these data concentrates on hypotheses of potential causal significance and makes use of advanced quantitative methods to test these hypotheses.